1. Field of the Invention
The invention relates to a rolling bearing.
2. Description of the Related Art
Many rolling bearings are used for various types of industrial equipment. A rolling bearing includes an inner ring, an outer ring, a plurality of rolling elements, and a cage. Among such rolling bearings, a ball bearing including balls as rolling elements offers particularly small rotational resistance. The rolling elements are interposed between the inner ring and the outer ring. The cage holds the rolling elements.
As a cage that holds balls, what is called a snap cage is known (see, for example, Japanese Patent Application Publication No. 2014-66346 (JP 2014-66346 A). FIG. 6 is a perspective view depicting a part of a conventional snap cage 90. The snap cage 90 has an annular portion 91 and a plurality of cage bars 92. The cage bars 92 extend from the annular portion 91 in an axial direction. A pair of the cage bars 92, 92 adjacent to each other in a circumferential direction forms a pocket 94 that holds a ball 93.
As depicted in FIG. 6, each pocket 94 has a pocket surface 95 that can contact the corresponding ball 93. The conventional pocket surface 95 is shaped along a spherical surface having a slightly larger diameter than the ball 93. Thus, a contact area between the pocket surface 95 and the ball 93 is large, leading to significant friction (high friction torque) between the cage 90 and the ball 93. The ball bearing, including balls as rolling elements, offers relatively small rotational resistance, but has been desired to offer further reduced resistance to deliver enhanced rotational performance.